Recommendations Not Showing
Easy Digital Downloads has an excellent extension called Recommended Products that can help you cross promote products throughout your store. Occasionally you may find that you have no recommendations, and this doc is intended to help you understand why.
Reason 1: Not Enough Data
Recommended Products analyzes the last 250 purchases on the site (every night) and based off those purchases, suggests other products that others have also purchased. This means that if your store is quite new, has been recently reset, or has very few transactions for any reason, you may not see any recommendations.
Reason 2: Already Purchased
On the checkout page, if the user is logged in and already owns a product then that product won't be recommended to them, even if it would normally have been. This makes room for other products that the customer may be interested in buying.
Reason 3: Lack of Theme Support
Some themes simply choose not to render them on the Checkout page.
More generally, Recommended Products relies on some hooks provided in the default EDD templates. If those templates are edited and those hooks removed, no recommendations will be printed.